Metal recovery method



' Aug. ze, 1969 J. w. Pam 3,463,632 i METAL RECOVERY METHOD Filed Feb.24. 1967 smfa//f Mazza-W 54H5 aar INVENTOR [f4/02651 swva/x/Wsfgz/United States Patent O 3,463,632 METAL RECOVERY METHOD Jack W. Petty,1115 Arbor Dell Road, Los Angeles, Calif. 90041 Filed Feb. 24, 1967,Ser. No. 618,458 Int. Cl. C22b 1]/02, 7/02; C10b 57/04 U.S. Cl. 75-83 4Claims ABSTRACT OF THE DISCLOSURE A method of obtaining precious metalsby heating oil shales to drive off oily vapors containing preciousmetals and bubbling the vapors through a bath of a molten alkali metalchloride.

Background of the invention This invention relates to the metallurgicalart and more particularly to a method of recovering metals from oilshales (kerogen), tar sands, carbonaceous material, and naturalpetroleum. When oil shales are mentioned hereinafter, tar sands, naturalpetroleum, and carbonaceous materials are included in this phrase.

Although the present invention should not be limited to those usesspecifically described herein, it has been found to have exceptionalutility in recovering gold, silver, and other precious metals fromvapors, gases, entrained liquids and solids obtained by heating andretorting oil shale (kerogen), tar sands, carbonaceous materials, andnatural petroleum. When the term vapors is mentioned hereinafter, it istaken also to include gases,

3,463,632 Patented Aug. `26, 1969 remove carbon, coke, adventitiousmineral particles, and the like which may enter the system from theretort. The filtered molten salt is returned to the bubble tower at aconvenient point above the molten salt level in the bubble tower. l

Types of retorts other than retort 3, such as the U.S. Bureau of Minesgas combustion type,Union Oil Company rock pump gas combustion retort,etc., which depend upon partial burning of the oil shale may also beused. The oily vapors and combustion products formed are collected atthe retort vapor exit 6 and then through tube 6 into the molten saltbath. AnotherI suitable method is to maintain a partial vacuum in thebubble tower so that oily vapors, etc. are drawn through the moltensalt.

In the event that natural petroleum is being processed, hot vapors,liquids, etc. from the pipe still are forced through the molten salt inthe bubble tower. However,

@trained liquids, and solids. 1t has been discovered that such vaporscontain gold and silver.

Summary of the invention In accordance with the present invention, goldand silver are removed from such vapors to reduce production costs ofpetroleum compounds. The method of the invention includes the step ofcontacting a molten alkali metal chloride in a liquid state with an oilyvapor derived from oil shale wherein the molten chloride salt has thecapacity of combining with the metals to be recovered.

The above-described and other advantages of the present invention willbe better understood from the following description when considered inconnection with the accompanying drawings.

Brief description of the drawing In the drawing, the view isdiagrammatic of the apparatus employed with the method of the presentinvention.

Description of the preferred embodiments In the drawing, an oil shaleretort 3 is located in a furnace 1. Retort 3 has an inlet passageway 4and an out let passageway 5. Shale is heated in retort 3 and vaporscollected and transmitted via a pipe 6 to the bottom of a bubble tower 7containing a molten chloride salt. Tower 7 has an inlet at 8 and anoutlet at 9. A condenser 10 is provided to condense oily vapors that arepassed from tower 7 to condenser 10. Bubble tower 7 s heated in afurnace 2.

In the tube leading from the bubble tower 7 to condenser 10, a vacuumpump 13 is incorporated. The vacuum pump 13 is used to facilitate theliow of oily vapors through the molten salt. Also, after passage throughthe molten salt, oily vapors are quickly transferred to the condenser,thereby reducing the tendency of the oily vapor to form coke in thebubble tower above the molen salt.

At a convenient place in the bubble tower near the bottom, provision ismade to circulate the molten salt by means of a suitable pump 12 througha filter 1.1 to

the temperatures employed are generally in the range of 400 F. to 1000F. or more. After passage through the molten chloride salt, the vaporsand hot petroleum are led into a fractionating column for furtherprocessing. See also Petroleum Products Handbook, Virgil B. Guthrie(McGraw-Hill, 1st edition, 1960, pages 1-11).

The molten salt bath in tower 7 may contain one or more of the moltenchloride salts of the.` metals in Groups I-A and II-A of the PeriodicTable as set forth on page 59 of Handbook of Chemistry sixth edition, byN. A. Lange (Handbook Publishers, Inc., 1946, Sandusky, Ohio). Modifyingsalts, such as NaOH, Na2CO3, NaCN, etc., and their potassiumcounterparts, may also be used in order to control molten salttemperatures, viscosities, and pH values.

Alternatively, the molten salt path in tower 7 may actually be two ormore salts. Thesel salts may be in the said groups of the Periodic Tableaforesaid. For example, KCl and NaCl chlorides may be used together. Li,Na and K chlorides may also be used together.

Example Oil shale is heated in retort 3 to a temperature of 850" F. ormore. The oil shale temperature should be sufficiently high to drive offoily vapors and yet be low enough to minimize breakdown of the oilyvapors. Li, Na and K salts are then used in tower 7, in proportions of50%, 25% and 25% by weight, respectively. They are also heated to atemperature of 850 F. or more, their melting point being approximately760 F. LiCl, NaCl and KCl are used.

It will be noted that the temperatures employed for this or any otherembodiment of the invention are not critical although best results areobtained Within the range of I850" F. to 1700 F. or more, such as thatobtained in gas combustion retorts.

When NaCl or KCl is used, each one is preferably heated to a temperaturein excess of 1475 F. or more. The melting point of NaCl is 1472 F. WhenKCl is used in tower 7, it is heated to a temperature of 1430 F. ormore, its melting point being 1429" F. Lower salt melting temperaturesmay be obtained by using approximately a 50-50 percent mixture of KCland NaCl. The melting point of this combination is approximately 1250oF.

None of the salt temperatures listed herein are critical. The salt bathsimply needs to be maintained in a molten state.

After petroleum vapors have been bubbled through the said molten saltsin tower 7, the molten salt is drawn off at 9 and allowed to cool to asolid state. Gold and silver may be recovered from the salt which isremoved from tower 7. Gold and silver in the product may then berecovered in any conventional manner. One method of recovery is todissolve the chloride salts in water and then filter (step one). Somesilver chloride will be found in the filtered material. The resultantsilver chloride may be recovered from the filtered material bydissolving in NH4OH and then retiltering. Addition of HNO3 to the aboveltrate will then reprecipitate AgCl. Metallic silver may then beproduced by cupelling the AgCl with lead. The filtrate from the initiallilter operation (step one), is acidied with HC1 and precious metals areprecipitated with zinc precipitate dust. Recovery of gold and silverfrom the Zinc produced may then be done in any standard manner asnormally employed in the mining industry for recovery of silver andgold.

The economics of the inventive process are attractive. For example,Colorado shale oil has a gold and silver content of approximately ftycents per barrel. Brea, Calif., natural petroleum approximatelytwenty-five cents per barrel, and Santa Maria, Calif., tar sandsapproximately forty-six cents per barrel. It is my experience that whenproceeding in accordance with the invention, a substantial proportion ofthe gold and silver contained in the kerogen content of the oil shaleappears in the oily vapors issuing from the retorting process, and inturn, a substantial portion of that is captured by the molten salt andeventually made available as saleable metallic gold and silver. It maybe observed that my inventive process can be carried out withno realinterference with conventional methods for recovering oil from oilshale, and from the standpoint of heat consumption, the operating costsare low indeed. The salts used can readily be recovered substantially byevaporation completely from the step wherein the gold and silver isextracted so that makeup quantities from the system as a whole are low.It will be appreciated that my process is equally adaptable to processesin which oil shale is retorted and the oil therefrom is not necessarilyrecovered as a valuable constituent per se. This may occur with oilshales of high gold and silver content and relatively undesirable oilyconstituents, or where the retorted shale is the primary product of theprocess, being useful, for example, asa lightweight aggregate forconcrete or for solid fuel.

What is claimed is:

1. The method of obtaining a precious metal, said method comprising thesteps of: heating a precious-metalbearing oil shale to drive olf oilyvapors containing a precious metal; bubbling said vapors through a bathcontaining a major amount of a molten alkali metal chloride; coolingsaid bath to a solid state; and recovering said previous metal from saidcooled bath.

2. The method of claim 1 wherein said precious metal is gold or silver.

3. The method of obtaining a precious metal, said method comprising thesteps of contacting a bath containing a major amount of a moltenchloride of at least one metal from Group I-A or II-A of the PeriodicTable with an oily vapor containing the precious metal to be recovered;and recovering said precious metal from said bath.

4. The method of claim 3 wherein said metal is gold or silver and saidbath contains lithium chloride, sodium chloride, and potassium chloridein proportions of 25% and 25%, respectively, by Weight, said chloridesbeing in the molten state.

References Cited UNITED STATES PATENTS RICHARD O. DEAN, Primary ExaminerU.S. Cl. X.R. -118

